This invention relates to oral compositions for use as dentifrices, topical solutions or pastes, desensitizers, prophylactic pastes, mouthwashes, disintegratable tablets, oral bands, cavity sealers, gels for ultrasonic treatment, gels for iontophoresis, dental flosses, chewing gum and the like. More particularly, this invention relates to oral compositions which contain a relatively highly soluble stannous compound such as stannous fluoride, a relatively difficultly soluble stannous compound such as stannous pyrophosphate, a phytic acid compound, and optionally, a fluorine compound and which are effective for the prophylaxis of dental caries and paradental diseases as exemplified by increased acid resistance of the tooth enamel treated therewith. It is well known that stannous compounds, when applied in the form of a solution or the like, can provide tooth enamel and dentin with an improved acid resistance due to the action of stannous ions. It is also known that when teeth are treated with those solutions additionally containing fluorine ions, for example, those containing stannous fluoride SnF.sub.2 or stannous chloride fluoride SnClF, not only the acid resistance of the tooth enamel is improved by stannous ions, but fluorine is also taken up by the tooth enamel, with outstanding results of caries inhibition, caries control, desensitization of hypersensitive dentin. (See J. C. Muhler et al, J.A.D.A., 51, 665 (1955)).
For the above reason, it was a common practice to apply stannous compound solutions to teeth or to blend stannous compounds into oral compositions such as dentifrices. Unfortunately, stannous compound solutions are not stable during storage and active dissolved stannous ions are likely to deactivate. Aqueous solutions of stannous fluoride are most widely used, but readily show a reduced efficacy in caries prophylaxis because as a result of hydrolysis or atmospheric oxidation, stannous ions contained therein tend to be converted into inert tin compounds (insoluble tin hydroxide, tin oxide, tin oxyfluoride, stannic tin compounds, etc.) which cannot produce the above-mentioned effect, and consequently the quantity of active dissolved stannous ions is considerably reduced. The lower the concentration of stannous fluoride is and the higher the storage temperature is, the more outstanding this tendency is. In the case of dentifrices containing stannous fluoride, stannous fluoride tends to react with other ingredients to form insoluble tin hydroxide, tin phosphate and the like, and soluble but highly stable complexes, resulting in a reduced quantity of active free stannous ions. This tendency is outstanding at pH 6.0 or higher. Furthermore, hydrolysis or dissolved oxygen causes Sn.sup.2+ in dentifrices to be oxidized into Sn.sup.4+. This causes a further reduction of the quantity of active dissolved stannous ions. Accordingly, the effect of blending stannous fluoride into dentifrices is not fully attained.
To prevent reduction of the quantity of active dissolved stannous ions during storage, a variety of attempts have been made. For instance, U.S. Pat. No. 2,946,725 and British Pat. Nos. 804,486 and 845,611 disclose a dentifrice containing a stannous compound, said stannous compound being difficultly soluble but capable of dissolving to supply at least 10 but not more than 1000 parts per million of stannous ions when in association with water, and being present in said dentifrice in an amount sufficient to provide said stannous compound in undissolved and undissociated form. These difficultly soluble stannous compounds such as stannous pyrophosphate, stannous metaphosphate and stannous tartrate are blended as a "reservoir" into dentifrices together with soluble stannous compounds such as stannous fluoride. The difficultly soluble stannous compound serves to supply a small quantity of stannous ions for a prolonged period of time to maintain the concentration of stannous ions constant. Another approach is to stabilize stannous ion by adding a certain type of organic chelating or complexing agents. Examples of such agents are carboxylic acids such as malic acid, citric acid and their salts as disclosed in U.S. Pat. No. 3,282,792; hydroxyethyl nitrilodiacetic acid and its salts as disclosed in U.S. Pat. No. 3,544,678; aldonic acid and its derivatives as disclosed in U.S. Pat. No. 3,105,798; and methane diphosphonic acid, ethane-1-hydroxy-1,1-diphosphonic acid and their derivatives as disclosed in U.S. Pat. No. 3,549,677 and British Pat. No. 1,160,640.
However, when difficultly soluble stannous compounds are blended as a "reservoir" particularly into relatively viscous systems such as dentifrices, gels and prophylaxis pastes, such compounds cannot always have a sufficient capability of supplying dissolved stannous ions, resulting in a considerable reduction of active dissolved stannous ions with time. Furthermore, the acid resistance of tooth enamel is not fully improved as shown in Experiments described below.
Stannous compounds, particularly fluorine ion-containing stannous compounds such as stannous fluoride produce an effect of improving the acid resistance of the tooth enamel to some extent. However, such stannous compounds are not fully effective when used alone.
Other investigations have been made on a variety of compounds having caries inhibitory effect. For example, an attempt was made to use sodium and potassium phytates to reduce the the solubility of hydroxyapatite in acid. However, the effect of these phytates has not been generally recognized. Other examples using phytic acid are British Pat. No. 1,384,375 which discloses an oral hygiene composition comprising a divalent metal salt of phytic acid such as calcium phytate mixed with a monofluorophosphate, and British Patent No. 1,408,922 which discloses an oral composition comprising two separate phases, one phase containing a water-soluble calcium compound and the other phase containing a water-soluble organic or inorganic phosphoric acid compound such as phytic acid and optionally, a water-soluble fluorine compound. However, the evaluation of these compositions has not been widely established. U.S. Pat. No. 3,934,002 also discloses toothpastes containing sodium phytate. British Pat. No. 1,222,197 discloses the use of inorganic or organic phosphorus compounds.